Wireless data interface system for fixed point-to-point communications

ABSTRACT

A system for transmitting process control information from remote sites is disclosed. In one embodiment, data is collected by a remote monitoring device or devices and transmitted to a first Cellular Digital Packet (“CDPD”) modem via one or more RS232 interfaces. The applications program in the first CDPD modem transmits a signal to a second CDPD modem initiating communications. The applications program in the second CDPD modem returns a signal, indicating the status of the interface. Data transmission is initiated when the status of both serial data interfaces is established.

TECHNICAL FIELD

The present invention relates generally to a communications system and,more specifically, to an apparatus and method for implementing acommunications interface protocol using existing Cellular Digital PacketData (“CDPD”) transmission equipment to implement point-to-pointcommunications. More specifically, the invention relates to an apparatusand method of monitoring data collected by instrumentation such astemperature, pressure and flow meters located at sites remote from theprocess control computer, display or programmable logic controller towhich the information is to be transmitted.

BACKGROUND

Collecting and monitoring data from a variety of locations for inputinto a central processing unit is a required function in a wide varietyof applications. For example, in a chemical processing plant, such as arefinery, a variety of process parameters such as temperatures,pressures and flows are continuously or intermittently monitored andrecorded. Similarly, in oil and gas production parameters such aspressures, flows and valve positions are measured and monitored.Typically, these parameters are measured at different locations in theparticular process, and in some cases the instrumentation may be locatedat a remote site. Measurements are normally collected by theinstrumentation as analog signal that is converted to a digital formatand subsequently transmitted to a computing device such as aprogrammable process controller or process control computer viadedicated hard wired serial data interfaces. However, in the case wherethe instrumentation is located at a remote site, it may be difficult orcost prohibitive to provide the direct hard wired connection between theserial data interface at the particular instrument's location and theinterface at the particular computing device. On the other hand,wireless transmission of digital data over long distances has heretoforeproven unreliable.

Cellular Digital Packet Data (“CDPD”) is a wireless communicationsprotocol that folds streams of data into envelopes or packets that aretransmitted at very high speeds during pauses in cellular phoneconversations. This permits the use of existing cellular systems as ameans of data transmission. CDPD allows data files to be assembled intopackets and transmitted via idle channels of existing, butCDPD-upgraded, cellular voice networks. CDPD allows the transmission ofdata at 19.2 Kbps over an enhanced cellular network. Adding CDPD to anexisting analog cellular system allows cellular systems to transmit dataeight times faster without the necessity of creating a completely newdigital system.

In practice, packet data is transmitted in a wireless mode usingbandwidth of the Advanced Mobile Phone Service (“AMPS”) which operatesas the communications infrastructure for analog cellular radio. Digitalcellular is referred to as D-AMPS. CDPD specifications are publishedthrough the CDPD Forum and follow OSI (Open Systems InterconnectionProtocol) guidelines. CDPD technology provides connectivity up to thenetwork layer and is an overlay system that operates on AMPSfrequencies.

The RS232 serial interface provides a serial data connection between twodevices over dedicated wires. The interface defines up to 26 linesbetween two devices. One line carries the data and the others carrysignaling information. Signaling is achieved by the lines through binarystates, either “ON” or “OFF.” Some lines are defined for data and somefor signaling. Thus, data transmission can be controlled simultaneous byboth the sending device and the receiving device.

For example, the sending device can query the receiving device as towhether it is ready to receive data by setting the signal high on a linecalled Ready To Send (“RTS”). The receiving device can, in turn, replythat it is ready to receive data by setting the signal high on the ClearTo Send (“CTS”) line. After these conditions are satisfied, by devicescan begin data transmission over the data lines a communication speeds.

SUMMARY OF THE INVENTION

The present invention provides a system for point-to-point communicationof digital data between devices utilizing RS232 interfaces. In oneembodiment, process data, such as temperatures, pressures and flows aremonitored at remote locations. The data is converted from an analogsignal to a digital format and transmitted to a wireless modem via anRS232 serial data interface associated with the particularinstrumentation. The data is then transmitted from the first wirelessmodem to a second wireless modem. The second wireless modem communicatesthe information to a device such as a process control computer orprogramable logic controller.

Wired RS232 applications conduct data communications between a senderand a receiver that are hard wired together. In a wired RS232 connectionbased application, several lines may simultaneously used to sendsignaling information; the signals on each line are detected by thesender and receiver instantaneously. On the other hand, in wirelessRS232 communications, instantaneous communication does not occur.Rather, information is transmitted with a delay of ranging from 0.5 to 4or 5 seconds. Furthermore, in wireless communications, modems canconnect to a large number of devices using the call establishmentmethodology programmed into the modems.

The present invention provides a method and apparatus for using wirelessmodems for point-to point transmission of serial data in an RS232 mode,that provide (1) logic establishing the sender and receiver and (2) asignaling and data transmission methodology that makes the wireless modetransparent to the applications. The method and apparatus of the presentinvention allows utilization of wired RS232 based applicationstransparently on wireless communication systems, and alleviates thedelay inherent in wireless communications without impacting thereliability of the system.

The invention provides a wireless point-to-point communications systemfor reliable and efficient digital data transfers as compared to priorart network interface protocols. In this regard, and in accordance withone embodiment, the invention utilizes a commonly availablecommunications protocol, such as RS232, or other accepted serialstandard to encapsulate digital data derived from an instrument, datacollector, or other signal acquisition means in a wireless signalcarrier. The serial protocol has built-in error correction and flowcontrol. The end-to-end interface is compatible with ordinary devicessupporting the protocol. In addition, the cellular communicationsinfrastructure provides a reliable backbone with call switching androuting of the data to its intended destination. The RS232 data and flowcontrol signals are encapsulated in a CDPD carrier supported in existingcellular infrastructure. Since RS232 is widely accepted and supported bya plurality of data acquisition and processing systems, the interfaceprotocol provided is reliable and efficient.

The present invention is particularly adaptable to systems incorporatingremote data collection devices such as process control systems,environmental monitoring systems, pipeline monitoring systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG.1(a) is a schematic illustration of a monitoring system utilizingstandard, wired RS232 data transmission;

FIG. 1(b) is a schematic illustration of a system employing the wirelessdata transmission of the present invention;

FIG. 2 is an illustration of components of a CDPD. utilized in thepractice of the present invention;

FIG. 3 is a tabular illustration of the configuration of theconfiguration of two of the lines of the serial data transmission deviceof the present invention;

FIG. 4 is an illustration of the timing of the sequence of steps in datatransmission utilizing the present invention;

FIGS. 5(a) and 5(b) are a flowchart for the transmitting applicationsdriver utilized in the practice of the present invention;

FIGS. 6(a) and 6(b) are a flowchart for the receiving applicationsdriver utilized in the practice of the present invention;

FIGS. 7(a) through 7(e) are a flow chart for control of the initiatingCDPD modem as utilized in the practice of the present invention;

FIG. 8(a) through 8(d) are a flow chart for control of the receivingCDPD modem as utilizedin the practice of the present invention; and

FIGS. 9(a) and 9(b) are a schematic representation of one embodiment ofthe system of the present invention.

DETAILED DESCRIPTION

Referring now to FIG. 1(a), a system utilizing standard RS232 datatransmission is illustrated. In the illustrated embodiment, monitoringdevices 10, measure process parameters such as temperatures, pressuresand flows. The information is normally collected by meters such as atemperature, pressure, or flow meter which typically output an analogsignal that are converted to a digital format and subsequentlytransmitted via wired RS232 interfaces to 14 to a computing device 16such as a computer, programmable logic controller or dataconcentrators/multiplexers for storage and processing.

FIG. 1(b) illustrates a data transmission system utilizing the presentinvention. Data is retrieved from remote monitoring devices 10 andtransmitted to a CDPD modem 18 via RS232 interfaces 14. CDPD modem 18transmits the information via cellular radio to a second CDPD modem 18′which, in turn, transmits the information via RS232 interfaces 14 tocomputing device 16. As noted above, the computing device may be aprogrammable logical controller, a process control computer or dataconcentrator/multiplexer for storing, processing and or displaying theinformation.

Referring now to FIG. 2, three components of the CDPD modem 18 areschematically illustrated. The CDPD modem 18 includes a SubscriberIdentity Module (“SIM”) 20, a Mobile Application Subsystem (“MAS”) 22and a Subscriber Unit (“SU”) 24. The mobile application substation 22interfaces with the end user application and the subscriber unit 24manages the air interface. In some applications, the SIM is a “smart”card that is inserted or installed in a cellular phone that contains allsubscriber-related information. The SIM facilitates communications froma valid cellular telephone because the subscriber data is used tocomplete telephone communications rather than the internal serial numberof the telephone. In one embodiment, the present invention provides anenhancement to the SIM with a standard RS232 interface that increasesthe distance that digital data can reliably and accurately betransmitted via cellular communications and supports multiple standardswithout modification.

FIG. 3 is a tabular illustration of the configuration of two of theRS232 interface lines or pins utilized to implement data transmission inaccordance with the present invention. In order to initiate datacommunications, the initiating application sets a “HIGH” signal on afirst line 26. The program in the modem on the initiation side of thetransmission decodes the signal and sets the status of the line in theline entry of the table to “SEND” and the value of the line to “HIGH.”The entire table 26 is transmitted by the modem 18 on the initiatingside as one packet of data. When the receiving modem receives thepacket, it changes the status of the entry for the first line in thetable to “ESTABLISHED” on the RS232 interface. The receiving applicationmust then acknowledge the signal by setting the second line 28 high inthe same sequence, i.e., set the status an transmit the table as onepacket to the receiving modem. The initiating application then sets thestatus to “ESTABLISHED” on the RS232 interface. When both lines are seenas “HIGH” and “ESTABLISHED” by the initiating application, theinitiating modem starts data transmission.

The data to be transmitted is concatenated to a signaling packet on theinitiating side and the packet is transmitted. Since both lines are“HIGH” and “ESTABLISHED,” the receiving modem accepts the data. ACyclical Redundancy Check (“CRC”) is used by the receiving modem toconfirm the validity of the data. If the data passes the CRC check, itis accepted as valid. Since the wireless modems 18 and 18′ providewireless error correction, duplication of this function is not required.Incorporation of the CRC, however, makes error checking consistentbetween a wired and wireless application. Through the combination of aminimal logic set and a minimal set of signaling data as set forth abovethe present invention provides transparency of the wireless link to theapplication, the same reliability as a wired link for the applicationand a minimal program size that is important for such applications.

Referring now to FIG. 4 the timing of the sequence of steps in datatransmission utilizing the present invention is schematicallyillustrated. First, the RTS line is pulled “high” on the RS232 interfaceon the initiating side. Next, the CTS line on the RS232 interface ispulled “HIGH” after receipt of the table 26. After the table 26 has beentransmitted back to the initiating modem 18 as described above, datatransmission commences. Upon successful completion of data transmission,i.e., when the receiving application detects the end of text in thedata, it sets the signal “LOW” on the CTS line, and initiates the samesequence of signaling to de-establish the lines.

FIGS. 5(a) and 5(b) are a flowchart for the applications driver for theinitiating modem. As illustrated, when the application is stated thefirst step is to check the status of the RS232 interface (step 102). Ifthe port is busy, a busy signal is returned to the application (step104). If the port is not busy, the application checks to determinewhether the RTS line is high (step 106). If the RTS line is set high, abusy signal is returned to the application (step 108). If the RTS lineis not set high, the port status is set busy (step 110) and the RTS lineis set high and table 30 is transmitted as described above (step 112). Atimer is initiated (step 114). If the timer times out before receipt ofthe table 26 from the receiving application, the port status is set to“ERROR” and the error status is returned to the application (steps 116and 118). If the table 26 is received by the initiating application withthe CTS line set high, the timers are reset (step 124) and datatransmission is initiated.

When the receiving application detects the end of text in the datatransmission it initiates a timer (step 128). If the applicationreceives a CTS “LOW” before the timer times out, the timers are reset(step 130) and the RTS line is set low (step 132). If the timer timesout before the CTS “LOW” is received, the port status is set to “ERROR”(step 134) and the error status is returned to the initiatingapplication (step 136). Assuming that the RTS “LOW” signal is confirmedby the initiating device before the timer is timed out, the port statusis set open (step 138) and a signal indicating successful transmissionis transmitted to the initiating application (step 140). If the RTS lowis not confirmed prior to the timer timing out, the port status is setto “ERROR” (step 142) and the error status is transmitted to theinitiating application (step 144).

Referring now to FIGS. 6(a) and 6(b) a flowchart for the applicationsdriver for the receiving application is illustrated. After theapplication is started, the status of the port is checked (step 200) andif the port is busy a return busy signal is returned to the application(step 202). If the RTS line is set low, a return “IDLE” signal isreturned to the application (step 204) If the RTS line is set “HIGH” theport status is set “BUSY” (step 206), the CTS line is set high (step208), and table 26 is transmitted to the initiating application. A timeris initiated (step 210) and if a data transmission is detected on theport before the timer times out, the data is read (step 214) and thetimer reset (step 216). If no data transmission is detected on the portbefore the timer times out, an error signal is returned to theapplication (step 212).

After the receiving application detect the end of text in the data, itsets the signal in the CTS line “LOW”, transmits the data in table 26(step 218) as described above to the initiating application and sets atimer (step 220). If the receiving application receives confirmationthat the RTS line is set low prior to timing out, the port status is setas “OPEN” (step 222) and a successful data receive signal is returned tothe initiating application (step 224). If confirmation is not received,and if the timer has timed out, the port status is set to “ERROR” (step226) and a return error signal is transmitted to the initiatingapplication (step 228).

Referring now to FIGS. 7(a) through 7(e) a flow chart for the CDPD.modem control for the initiating modem is illustrated. The status of theRTS line is checked (step 300), and if the RTS line is set high thestatus of the RTS line is mapped as “SEND” in the application buffer(step 302) and the application buffer is copied to the communicationstransmit buffer (step 304). The transmit buffer is then transmitted tothe receiving modem as a UDP (“User Data Protocol”) message, (step 306)and a timer is set (step 308). If a message is received from thereceiving modem in the receive buffer (step 310), the receive buffer iscopied to the application buffer (step 312) and the timer is reset (step314). If the timer times out prior to the receipt of a message from thereceiving modem (step 316) the number of attempted transmissions iscompared to a predetermined maximum number of transmissions (step 318).If the number of attempted transmissions exceeds the predeterminedmaximum an error message is returned to the application (step 320).

After the receive buffer is copied to the application buffer, the statusof the RTS and CTS lines in the application buffer is checked (step322). If the RTS line status is set to “ESTABLISHED” and the CTS linestatus is set to “SEND”, the predetermined number of permissibletransmission attempts is reset (step 324) and the CTS line is set “HIGH”(step 326), otherwise control is returned to step 306. Upon receipt ofdata, the data is read from the data line into the application buffer(step 328) and the CTS line status is set as “ESTABLISHED” in theapplication buffer (step 330). The application buffer is copied to thetransmit buffer (step 332 ), transmitted as a UDP message (step 334) anda timer is set (step 336).

If a message is received from the receiving modem in the receivingbuffer (step 338), before the timer times out, the contents of thereceiving buffer are copied into the applications buffer (step 340). Ifthe timer times out prior to the receipt of a message from the receivingmodem (step 342), the number of attempted transmissions are compared toa predetermined maximum number of transmissions (step 344). If thenumber of attempted transmissions exceeds the predetermined maximum, anerror message is returned to the application, otherwise control isreturned to step 334. After the contents of the receiving buffer iscopied into the applications buffer (step 340), the timer is reset andthe line status in the application buffer is checked for RTS“ESTABLISHED” and CTS “LOW” (step 344). If these conditions are met, theCTS line is set “LOW” (step 346). If the line status in the applicationbuffer for RTS is not “ESTABLISHED” or if CTS is not set “LOW”, controlis returned to step 334.

After the CTS line is set “LOW” in step 346, the RTS line is checked fora “HIGH” condition (step 348) and the maximum number of permissibleattempted number of attempted transmissions is reset (step 350). If theRTS is “LOW,” control is returned to step 348. After the number ofpermissible attempted transmissions is reset in step 350, the linestatus for RTS in the applications buffer is set “LOW” (step 352). Theapplications buffer is copied to the transmit buffer (step 354), thetransmit buffer is transmitted as a UDP message (step 356) and a timeris set (step 358). If a message is received from the receiving modem inthe receiving buffer (step 360) prior to the timer timing out (step362), the contents of the receiving buffer are copied into theapplication buffer (step 364) and the timer is reset (step 366). If thetimer times out (step 362 ) the number of attempted transmissions iscompared to the maximum permissible number (step 368). If the number ofattempted transmissions exceeds the maximum permissible number, an errormessage is returned to the application, (step 370); if not, control isreturned to step 356.

After the timer is reset in step 366, the line status in theapplications buffer is checked for RTS “LOW” and CTS “LOW” (step 372).If these conditions are not met, control is returned to step 354, if theconditions are met, a signal indicating a successful transmission isreturned to the application (step 374).

Referring now to FIGS. 8(a) through 8(d), the modem control for thereceiving modem is schematically illustrated. The receiving modem checksto determine whether the modem is in use (step 400) and if so, signals areturn (step 402). If the modem is not in use, the application checksfor a new message in the receive buffer (step 404). If a message ispresent in the receive buffer, the contents of the receive buffer arecopied (step 406) to the applications buffer and the line status ischecked for RTS “SEND” and CTS “LOW” (step 408). If these conditions aremet, the RTS line is set “HIGH” (step 410) and the status of the CTSline is checked for a “high” status (step 412).

If the line status of the CTS is high, the line status in theapplications buffer is set as RTS “established” and CTS “send” (step414). The contents of the application buffer are copied to the transmitbuffer (step 416) and transmitted to the initiating modem (step 418) asa UDP message. A timer is set (step 420) and the receive buffer ischecked for receipt of a message from the transmitting modem (step 422).If a message is received from the transmitting modem before the timertimes out (step 424), the message is copied from the receive buffer intothe applications buffer (step 426). At this time, the timer has timedout and the number of attempted transmission has exceeded thepredetermined maximum number of allowable attempted transmissions, (step428), a error signal is returned to the application (step 430). If thetimer has not timed out, control is returned to step 422, or if thetimer has timed out and the predetermined maximum number of attemptedtransmissions has not been exceeded, control is returned to step 418.

After the contents of the receiving buffer have been copied into theapplications buffer in step 426, the timer is reset (step 432) and theline status is checked for RTS “established” and CTS “established” (step434). Data from the dateline is written to from the dateline on the portto the application (step 436). The status of the CTS is check for “low”(step 438) and if this condition is met, the predetermined allowablenumber of attempted transmissions is reset, (step 440) and the CTSstatus is set to “low” in the applications buffer, and the contents ofthe applications buffer is copied to the transmit buffer fortransmission as a UDP message (step 444). a timer is set (step 446) andthe receive buffer is monitored for receipt of a message from thetransmitting modem (step 448). If the timer times out prior to receiptof a message from the transmitting modem, (step 450) the number ofattempted transmissions is compared to the predetermined allowablenumber of attempted transmissions (step 452) and if the maximumallowable number of attempted transmissions is exceeded, an error signalis returned to the application (step 454).

After a message has been received from the transmitting modem, (step448), a copy of the received buffer is copied to the application buffer,(step 456) and the line status is checked for CTS “low” and RTS “low”(step 458). If these conditions are met, the contents of the transmitbuffer are transmitted (step 460) and a “successful receive” message isreturned to the application. If the line status conditions are not met,control is returned to step 446.

Through the combination of a minimal logic set and minimal signalingdata as set forth above, the present invention provides a transparentwireless link between RS232 interfaces with the same or equivalentreliability as a hard wired link. Further, the present inventionprovides these features with a minimal program size, a feature that isimportant in the applications of interest.

Turning now to FIGS. 9(a) and 9(b) the invention is illustrated in thecontext of controlling the operation of a control valve on an offshoredrilling platform. Offshore drilling platforms are, in some cases,remotely operated and controlled for several months at a time. In suchcases the control functions may be performed using the wireless datainterface of the present invention. Resident on the platform 500 is aprocess vessel 502 such as a pumping tank or separator. Liquidhydrocarbons enter the process vessel 502 through control valve 504. Thevessel 502 is equipped with a level control sensor 506. In accordancewith one embodiment of the present invention, the level of fluid invessel 502 is monitored from a remote control center which, in turn,controls the operation of valve 504 via wireless telecommunications.Preferred characteristics of the wireless communication and controlsystem in such an application include: (1) response time of less thantwo seconds, more preferably less than one second; (2) transfer ofinformation packets of from one to sixteen bytes with a high degree ofaccuracy; (3) immediate identification of error conditions in eachinformation transmission; and (4) adaptability of the system to existinghardware and equipment.

By way of illustration, level control sensor 506 measures the level invessel 502. At preprogramed one second intervals the output from thelevel control sensor 506 is transmitted to CDPD modem 512(a) via RS232cable 510(a). CDPD modem 512 transmits the signal from the level controlsensor 506 to a central control station 516 where it is received by CDPDmodem 512(b). The signal is then transmitted to programmable controller514 which, in turn, responds with a control signal transmitted to CDPDmodem 512(b) through RS232 cable 510(d). The control signal istransmitted by CDPD modem 512(b) to modem 512(a) which communicates thesignal to controller 508 which, in turn, adjusts the position of controlvalve 504.

As illustrated, the CDPD modems 512(a) and 512(b) each have two serialports, corresponding to the monitored variable, in this case the fluidlevel in vessel 502, and the control function performed by programmablecontroller 514. In accordance with the present invention, the packetformat utilized to transmit the measured variable and control signals isaugmented with a port number. Each information packet is input into abuffer dedicated to the particular port. When modem 512(a) or 5132(b) isavailable for transmission, information packets stored in the buffersassociated with the respective ports are combined and transmitted. Thereceiving modem directs the packets to the designated port as indicatedby the port number incorporated into the packet. The addition of theport identification to the information packet allows modems 512(a) and512(b) to each support two ports, thus eliminating the need for multiplemodems at the platform 500 and central control station 516. It will beappreciated by those skilled in the art that the system described in theabove example can be readily expanded to accommodate measurement andcontrol of numerous process parameters and functions through the use ofmultiple RS232 ports connected to one CDPD modem located at the remotesite and a second CDPD modem located at a central control center. Sincethe system of the present invention is capable of supporting numerousapplications, overhead is shared among the various monitoring andcontrol devices resulting in a substantial gain in efficiency.

While the present invention has been disclosed and discussed inconnection with the above-described embodiment, it will be apparent tothose skilled in the art that numerous changes, variations andmodifications within the spirit and scope of the invention are possible.Thus, while the invention has been described in the context oftransmitting information from remote instrumentation to a centralprocessing center or computing device, the invention will beadvantageously used in other applications where point-to-pointcommunications between remote devices utilizing digital serial datainterfaces to transmit and receive information. Accordingly, it istherefore, intended that following claims shall encompass suchvariations and modifications.

What is claimed is:
 1. A method for providing wireless monitoring, themethod comprising: receiving data from a monitoring device according toa physical layer signaling protocol that includes RS-232; receiving acontrol signal having a HIGH value on a line from the monitoring deviceto initiate communication with a computing device; setting status of theline to SEND; changing the status of the line to ESTABLISHED uponreceiving acknowledgement from the computing device; and transmittingthe data to a computing device according to the physical layer signalingprotocol over a wireless point-to-point link using a cellular protocol,wherein the wireless link is transparent to an application that resideson the computing device and utilizes the physical layer signalingprotocol.
 2. A method according to claim 1, wherein the cellularprotocol includes a Cellular Digital Packet Data (CDPD) protocol.
 3. Amethod according to claim 1, wherein the monitoring device in thereceiving step includes at least one of a flow measurement device, atemperature measurement device, and a pressure measurement device.
 4. Amethod for providing wireless monitoring, the method comprising:receiving data from a monitoring device according to a physical layersignaling protocol, which includes RS-232, over a wirelesspoint-to-point link using a cellular protocol, wherein the wireless linkis transparent to an application that resides on a computing device andutilizes the physical layer signaling protocol; receiving a packet fromthe monitoring device to initiate communication with the computingdevice, the packet indicating a status of a line of SEND and associatedvalue as HIGH; changing the status of the line to ESTABLISHED; receivingacknowledgement to establish the communication upon the computing devicesetting a second line to HIGH; and transmitting the data to thecomputing device according to the physical layer signaling protocol,wherein the wireless link is transparent to an application that resideson the computing device and utilizes the physical layer signalingprotocol.
 5. A method according to claim 4, wherein the cellularprotocol includes a Cellular Digital Packet Data (CDPD) protocol.
 6. Amethod according to claim 4, wherein the monitoring device in thereceiving step includes at least one of a flow measurement device, atemperature measurement device, and a pressure measurement device.
 7. Amethod for providing wireless monitoring, the method comprising:generating data by an application based upon measurements, theapplication complying with a physical layer signaling protocol thatincludes RS-232; sending a control signal having a HIGH value on a lineto a modem to initiate communication with the computing device, whereina modem sets status of the line to SEND and changes the status of theline to ESTABLISHED upon receiving acknowledgement from the computingdevice; and transmitting the data according to the physical layersignaling protocol to a modem, wherein the modem transmits the data tothe computing device according to the physical layer signaling protocolover a wireless point-to-point link using a cellular protocol, whereinthe wireless link is transparent to the application and to a receivingapplication that resides on the computing device and utilizes thephysical layer signaling protocol.
 8. A method according to claim 7,wherein the cellular protocol includes a Cellular Digital Packet Data(CDPD) protocol.
 9. A method according to claim 7, wherein themeasurements in the generating step include at least one of flowmeasurements, temperature measurements, and pressure measurements.
 10. Amethod for providing wireless monitoring, the method comprising:receiving data generated according to a physical layer signalingprotocol that includes RS-232 from a remote monitoring device via alocal modem over a wireless point-to-point link using a cellularprotocol; receiving a packet from the monitoring device to initiatecommunication with a computing device, the packet indicating a status ofa line of SEND and associated value as HIGH; setting a second line toHIGH to acknowledge establishment of the communication with themonitoring device; and processing the data according to an applicationutilizes the physical layer signaling protocol, wherein the wirelesslink is transparent to the application.
 11. A method according to claim10, wherein the cellular protocol includes a Cellular Digital PacketData (CDPD) protocol.
 12. A method according to claim 10, wherein themonitoring device in the receiving step includes at least one of a flowmeasurement device, a temperature measurement device, and a pressuremeasurement device.
 13. A method for providing wireless monitoring, themethod comprising: receiving, according to a signaling protocolincluding RS-232, a control signal having a HIGH value on a line from amonitoring device to initiate communication with a computing device;setting status of the line to SEND; and changing the status of the lineto ESTABLISHED upon receiving acknowledgement from the computing device,wherein data is transmitted to the computing device over a wirelesspoint-to-point link using a cellular protocol, and the wireless link istransparent to an application that resides on the computing device andutilizes the signaling protocol.